This invention relates to an improvement in methods and equipment for installing small diameter columns of granular material in soil, such as used to install granular drains, which allows repetition of the column forming procedure without requiring interruption to fill the tank supplying material to the hollow shaft cavity forming tool, and configuring the equipment to induces less stress in the column forming tool to minimize potential breakdowns due to the effects of stress repetition as compared to other apparatus applicable to the economic installation of small diameter granular columns.
Equipment used for economic installation of small diameter columns of granular material in soil, as disclosed in U.S. Pat. No. 5,647,690, has an oversized hopper to contain a larger volume of backfill material in conjunction with a cavity forming tool with a small cross-section to enable formation of more than one column in soil before interrupting the cavity forming operation to refill the tank containing excess backfill material, and includes means to interrupt the flow of material after each column is formed to avoid waste of excess backfill material which is retained in the tank for use in backfilling subsequent cavities to complete added columns.
The weight of multiple columns of material in the hopper positioned on the small sized cavity forming tool may require the tool to act as a column to support the weight of the backfill tank and its contents, which causes the tool to deflect in a manner which induces stresses that may cause the tool to fracture or otherwise render it not usable for forming and backfilling cavities in an uninterrupted manner, particularly where columns need to be relatively linear and have a reasonably predictable orientation. The equipment and controls related to limiting flow of backfill from the hopper may result in maintenance problems which can also result in costs related to interruptions in equipment use.
It is the object of this invention to reduce the cost of granular column installation and increase the durability of the cavity forming tool by reconfiguring equipment disclosed in U.S. Pat. No. 5,647,690, to enable installation of multiple columns using a procedure and apparatus configuration that enables supplying backfill material for one column at a time to an intermediate hopper during the time that the cavity is being formed, which avoids interruption to production, and minimizes the weight on the hollow shaft cavity forming tool by reducing the size of backfill tank used and minimizing detrimental stress on the tool and related costs of repair and loss of equipment use, and eliminates interrupting production to periodically replenish the tank with backfill material.